Submit 2.3.0 to CRAN

[sfirke]

CRAN asked for the fix to #555 (completed) to be submitted to CRAN "within the next few months." This gives a chance to incorporate any other changes we want to ship for the next version, 2.3. #527 and #301 would be good candidates if someone felt ambitious for adding features, otherwise I'll take care of:

• #540